Results tagged “ADSC” from The SIBYLS Beamline

Our detector is gone!

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It's gone! We boxed up our Q315 yesterday and sent it back to ADSC for an upgrade to the Q315r model.

 

160408_Q315gone.jpg

 

Essentially this is an upgrade to the amplifiers that read out the CCDs and the other associated electronics for getting the raw images to the detector computers for processing. The fiber optic tapers and CCDs will not be replaced. The overall benefits of this upgrade are an decrease in read-out noise, an increase in speed, and the ability to use stored dark current images. Here are some excerpts from a detailed comparison performed by James Holton:

          ampgain  eo_gain    readnoise  pixel  fog photons  allowable
detector  e-/ADU   e-/photon  e-/pixel    um      /100um2   redundancy
----------------------------------------------------------------------
Q315      12       7.3        27(swbin)  102.4     12.4         1.00
Q315       4       7.3        16(hwbin)  102.4      4.37        2.85
Q315R      4       7.3        11.5       102.4      2.26        5.51
M300HE     4?     11           7.7        73.2      1.71        7.29

"fog photons"/pixel is the number of extra background photons/pixel required to increase the noise in a pixel by the same amount as the read noise. Since the "fog photons" will add with redundancy, the far right column shows how many fold more images (relative to a Q315) you can spread the same total x-ray exposure over and get the same total read noise (as if you collected the data with "unit" redundancy on a Q315).  The Q315R will allow 5.5x more images than what we are doing now: 12 "fog photons"/pixel on a Q315 in swbin mode.

James goes on to compare the relative crysal sizes that will produce equivalent diffraction:

All things being equal (including the extent of radiation damage), the intensity of the spots and background are proportional to the crystal volume.  Doubling the crystal volume will double the signal (spot intensity) as well as double the background (in the ideal case of a "naked crystal" with no air scatter or other sources of background).  So doubling the crystal volume makes the noise (sqrt(signal+background)) go up by no more than sqrt(2).  Unless the crystal is bigger than the beam, or it is so thick that it attenuates the beam, radiation damage will be proportional to photons/um2, which has nothing to do with the crystal size.  This means that, for the same extent of damage, the signal/noise ratio goes as size^(3/2) if "size" is the linear dimension of the crystal.  That is, doubling the linear dimension of a "round" crystal will nearly triple the signal/noise (2.83x), and a 10% increase in the "size" (linear dimension) will increase signal/noise by 15%.

If we have some high-res spot with I/sig(I)=2 in the absence of any background or read noise, then there are (on average) 4 photons in that spot (4/sqrt(4) = 2).  Spots typically take up on the order of 25 pixels.  So, adding 0.1 "fog photon"/pixel (as on a Mar300HE) will make I/sig(I) of this spot drop from 2.0 to 4/sqrt(4+25*0.1) = 1.6.  Increasing the crystal size by 12.5% will increase the crystal volume by 42% and put 5.7 photons into this same spot (for the same exposure time and therefore the same amount of radiation damage) and bring I/sig(I) back up to 5.7/sqrt(5.7+25*0.1) = 2.0.  This means that the crystal size needed to achieve a given resolution limit on the Mar300HE is 12.5% larger than the crystal size needed to achieve the same resolution with an ideal photon-counting detector (such as the Pilatus). This is assuming there are no other sources of noise, including x-ray background.

Changing the read noise to 2 "fog photons"/pixel will make the I/sig(I) of this 5.7-photon spot drop from 2 to (5.7/sqrt(5.7+25*2)) = 0.76.  Bringing the signal up to 16.3 photons/spot will bring I/sig(I) up to 2.0 again.  This represents a ~3-fold increase in crystal volume (16.3/5.7=2.86) and a 42% increase in crystal size.  To put it another way, using the Mar300HE instead of a Q315R would let us get away with crystals 30% smaller in linear dimension for a given resolution limit (and given amount of damage).  Going from a Q315R to a Q315 (with 21 "fog photons"/pixel) will require 47.9 photons in the spot (47.9/sqrt(47.9+25*21) = 2.0) and another 43% increase 

detector    photons/spot   xtalsize
perfect          4.0     0.63 or -37%
M300HE           5.7     0.71 or -29%
Q270             7.8     0.78 or -22%
M300            12.2     0.91 or -9%
Q315R           16.3     1.00
Q315            47.9     1.43 or +43%

The take home message is that our new Q315r will be way better than that old Q315 peice of junk. We will now collect more accurate data in less time with smaller crystals.

 

Q315 Temperature Control

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The detector can be brought up to essentially room temperature (in order to gracefully shut it down or do other work on it) or brought down to -40°C (to minimize detector noise for data collection) using the “Quantum Console” program on the detector computers.

This figure shows a fairly typical screen image on the detector computers.

In the image shown, the “REMOTE Detector OP” program is already running (as a DOS window). If this program is not running, it needs to be run before the Quantum Console can control the detector modules. The shortcut to the program is highlighted by one of the white circles.

Once the “REMOTE Detector OP” program, hereafter the detector program, is running on all nine modules, you can control the detector temperature by running the Quantum Console program on any one of the detector computers. The shortcut for this program is highlighted by the other white circle.

When the Quantum Console starts, it will open a window that looks something like this:

Before you can do anything else, you need to click on “Connect to Detector Processes.” This will create a row of status reports and allow you to click on “ENABLE Temperature Control”, resulting in a window something like this one:

This window actually shows a temperature-change operation that is already under way, but all the essential parts are visible.

If all is as it should be, setting the temperature is fairly simple. To cool the detector down for operation, click “Ramp to Cold Operating Temp”. To warm it up, click on “Warm up Detector to +10°C”. Either one will gradually bring the detector to the desired temperature. Shifting by the whole range from +10°C to -45°C, in either direction, generally takes about an hour.

Unfortunately, it is occasionally necessary to restart the ADSC detector along with the associated software. This will summarize how that is done. We will assume that everything is up and running at the beginning of the process; starting when some component or other is down is essentially the same.

We’ll assume that this is only a short interruption and that we don’t have to worry about the detector vacuum.

Begin by bringing the detector to room temperature (or +10C) as described in “Detector Temperature Settings.”

Once the detector is warmed up, it can be shut down at the power switches —- it is not necessary to shut down the detector processes or other software first.

Turn the detector power switches (the green switches highlighted by the arrow) off from top to bottom. The main power switches should be turned on starting with the bottom power module, then the middle module, then the top module. The order does matter.

If you don’t have the “REMOTE Detector OP” processes running yet, this is the time to start them. Double click on the “REMOTE Detector OP” shortcut, and you should see a DOS window appear:

Even if you already had these processes running when you restarted the detector, they still must be sent a reset signal. We generally do this from a script. The script makes up part of /programs/beamline/nuke, so it can be found there, but for completeness, here is the one we’ve been using:

foreach module ( detector0 detector1 detector2 detector3 detector4 detector5 detector6 detector7 detector8 )
    # send the reset signal
    echo -n "$module restart "
    echo "restart" | sock_exchange.tcl $module 8038 1
    echo ""
end

Entering that script at a shell prompt at any of the BL12.3.1 Linux consoles should reset the whole group of detectors. (Since the BLU-ICE/DCSS control programs run on dataserver, that is a good place to run the script.) This reset signal will cause lots of activity on the “REMOTE Detector OP” windows:

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